P110S油管在无固相压井液中点蚀成因分析

Analysis of Pitting Corrosion Causes for P110S Tubing in Solid-free Well-killing Fluid

分析P110S油管在井下无固相压井液环境中发生点蚀的原因。经检测油管的合金成分和组织无异常;通过对压井液注入前后的化学性质和腐蚀产物的分析,判断压井液入井后有酸性物质混入,且腐蚀产物中存在CO_(2)腐蚀特征产物FeCO_(3);通过高温高压腐蚀模拟试验再现油管点蚀现象,确定了P110S油管在无固相压井液中的点蚀是因为井下CO_(2)溶入压井液后引起油管发生CO_(2)腐蚀。对于井下工况不甚明朗的作业管柱选材,建议依据前期探明的井下工况选用具有更高耐蚀性能的管材,提高管柱腐蚀冗余,从而避免管柱腐蚀失效带来的安全隐患和经济损失。

An analysis is conducted on the causes for the pitting corrosion of the P110S tubing in the environment of solid-free well killing fluid.The alloy composition and microstructure of the tubing are confirmed normal via relevant testing.Owing to analyzing the chemical properties and the corrosion products of the tubing as identified before and after the injection of the well-killing fluid,it is determined that some acidic substances are mixed with the well killing-fluid as being injected into the well,and there exists in the corrosion products FeCO_(3),a product with CO_(2)corrosion characteristics.Finally thanks to the hi-temperature,hi-pressure corrosion simulation test to reproduce the tubing pitting corrosion phenomenon,it is revealed that the above mentioned pitting corrosion of the P110S tubing is caused by the CO_(2)as dissolved in the well-killing liquid.Accordingly it is suggested that when selecting proper tubing as working string for a well which operation conditions are not so clear,tubular goods with higher corrosion resistance according to the in-well working conditions as identified before should be used so as to increase the corrosion redundancy of the string for avoiding any potential safety hazard and economic loss as caused by the failure of corroded string.